High speed variable displacement pump



APri] 1962 R. D. RUMSEY ETAL 3,028,814

HIGH SPEED VARIABLE DISPLACEMENT PUMP Filed Oct. 17, 1957 3 Sheets-Sheet1 54- J All: I53: Z5 O i 0 m I] fi A24 49 H n ,M /& 91 3 50 5e "J 72 58ZTf al P Eo/flzz Doug/a5 Ramsey April '10, 1962 ,R. D. RUMSEY- ETAL3,028,814

HIGH SPEED VARIABLE DISPLACEMENT PUMP Filed 001;. 17, 1957 3Sheets-Sheet 2 Fo/[lfl Doug/a5 Ramsey Emma/f 6. Mal/112L119 April 10,1962 R. D. RUMSEY ETAL 3,028,814

HIGH SPEED VARIABLE DISPLACEMENT PUMP Filed Oct. 17, 1957 3 Sheets-Sheet3 Lye .EZZZJLE Pol/112 Doug/as Ramsey Emmett 6. Manning b M %a43,028,814 HIGH SPEED VARIABLE DISPLACEMENT PUMP Rollin Douglas Rumsey,Buffalo, and Emmett C. Manning, Lockport, N.Y., assignors to HoudailleIndustries, Inc, Butialo, N.Y., a corporation of Michigan Filed Oct. 17,1957, Ser. No. 699,807 4 Claims. (Cl. 1(23-161) The present inventionrelates to improvements in constant pressure variable displacementpumps, and more particularly to pumps of this character which areautomatically adjustable in response to operating conditions andrequirements encountered during performance of the pump.

More particularly, the invention relates to improvements in rotary pumpshaving a rotor carrying a pumping means such as the type carrying radialpistons which are actuated by engagement with the inner surface of asubstantially circular enclosing pump chamber eccentrically located withrespect to the rotor. The displacement of the pump is varied by varyingthe eccentricity of the chamber with respect to the rotor. The inventioncontemplates improvements in the control of the positional displacementof the axis of the pump chamber between substantially zero displacementand full displacement to achieve a variation in pump output for constantpressure delivery. The invention also contemplates improvements whichobviate the difiiculties which occur with change in dimensions withtemperature variation. The problem of the generation of heat in pumps ofthe variable delivery type when the delivery is reduced to zero is alsoaccommodated to correct problems heretofore encountered.

An object of the invention is, therefore, to provide an improvedvariable displacement constant pressure rotary pump.

Another object of the invention is to provide a constant pressurevariable displacement pump which is capable of obtaining greaterstability during operation, and-freedom from vibration or chatter, andother difficulties encountered with variation in part dimensions withtemperature increase, and especially such as encountered due to thediiterence in expansion between the pump housing and the enclosed pumpparts.

Another object of the invention is to provide a pump of the type abovedescribed wherein improved positioning and control means are providedfor eccentrically locating the chamber surrounding the pump rotor forcon trolling the output displacement of the pump.

Another object of the invention is to avoid the problems of overheatingin a variable displacement pump when the displacement reaches zero andthe fluid passing therethrough reaches a minimum by providing a by-passsupply of fluid for cooling the pump.

A further object of the invention is to provide an improved pump of thetype wherein a rotor carries radially reciprocating pistons operatedwithin an eccentric pump chamber, and wherein the pump chamber caneasily and accurately be positioned with respect to the rotor.

Still another object of the invention is to provide a pressure balancedvalve plate for supplying fluids to a rotary pump wherein the surfacepressure between the valve plate and pump will remain substantiallyconstant regardless of changes in fluid supply pressure.

Another object of the invention is to provide for increased fluid supplypressure to a rotary pump to decrease cavitation effects without havingto supply a separate means for providing pressurized fluid.

Other objects and advantages will become more apparent with the teachingof the principles of the invention in connection with the disclosure ofthe preferred embodi- Stas atom 3,028,814 Patented Apr. 10, 1962 FIGURE2ais a sectional view taken along line Ila- Ila of FIGURE 1 and showingan end view of the valve plate;

FIGURE 3 isa sectional view taken along line IIIIII of FIGURE 1;

FIGURE 4 is a sectional View taken along line IVIV of FIGURE 1; and,

FIGURE 5 is a sectional view taken along line V--V of FIGURE 4.

As illustrated in FIGURES 1, 3 and 4, the pump is enclosed by a housing8 which may be provided with an outwardly extending flange 10 forpurposes of mounting the pump housing, such as by bolts inserted throughholes 12, 14 and 16 in the housing. The housing is preferably formed ofa casting which is suitably cored and tapped for attachment of thevarious elements to be described.

At one end of the housing is a circular opening 18 through which a pumpdriving shaft, not shown, will be extended for driving a pump rotor 20.A shaft seal 21 will surround the shaft and the seal is pushed againstthe rotor 29 by Belleville springs 19 held in place by an annular ring23 which is held against the housing 3 by screws 25. For enclosing therotor and other parts within a housing chamber 22 defined by thehousing, a housing cap 24 is attached to the end of the housing oppositethe opening 18. The housing cap is suitably clamped to the end of thehousing and secured thereto such as by bolts 26. A gasket 28 is providedto prevent leakage of fluid from within the housing. A shaftgasket 30 isalso provided which will surround the pump driving shaft in afluid-tight manner. This will permit the flow of cooling fluid throughthe housing in the manner which will later be described.

The pump rotor 20 is mounted Within the housing chamber 22 for rotationtherein, and is substantially cylindrical in shape. The rotor 20 has ashaft receiving socket 32 to which the shaft is connected for drivingthe rotor in rotation. Rotation will be maintained at a constant speed,and the variable displacement constant pressure output will be obtainedin the manner to be described.

A plurality of circumferentially spaced radially extending cylindricalholes are bored into the rotor as shown at 3-4. Fitted into each of thecylindrical bores are pistons 36 which are mounted for reciprocation ina generally radial direction to move into and out of the cylindricalopenings or cylinders 34 to cause a pumping action. The cylindricalbores are formed to angle forwardly. As may be observed in FIGURE 3, thepistons are thus canted forward in such a way as to produce as low anoverhanging couple as possible. 7

Intake fluid for the cylinders 34 is received through a fluid passageway38 in the rotor, as illustrated in FIGURES 1 and 2 with a separatepassageway provided for each cylinder bore 34. Passageway 38 (FIGURES 1and 2), is a circular passageway canted in the direction of rotation ofthe rotor 20 so that as the rotor turns the fluid is rammed into thecylinder chamber, thereby reducing the inlet pressure required toprevent cavitation. The canted passageway 38, as it breaks through theface 39 of the rotor, forms an elliptical opening. This feature isparticularly desirable on high speed pumps because it has been foundnecessary to run inlet pressure as high as psi. in order to force fluidinto the pumping chambers with axial passageways. The fact that thecanted channel is in the wrong direction for discharge flow isrelatively immaterial because at that time no cavitation danger exists.

The pistons are forced inwardly in their reciprocating movement by afirst inner modulating ring 40 which surrounds the rotor and iseccentric thereto in normal operating position. The modulator ring 40may be shifted in a lateral direction to vary its eccentricity withrespect to the rotor to thereby vary the displacement or effectiveoutput of the pump. For operating the pistons, rollers 42 are positionedbetween each of the pistons and the modulating ring 40 with the rollers42 positioned with their axis extending parallel to the axis of therotor 20 and engaging the outer ends 44 of the pistons and the innersurface 46 of the modulating ring 40. The rollers 42 remainsubstantially stationary during operation of the pump, inasmuch as themodulating ring is mounted for rotation, the rotary driving force isapplied to the piston and the ring is carried therewith by at least oneof the rollers 42 frictionally engaging the modulating ring 40 andcarrying it in rotation with the rotor.

For carrying the rollers 42 in place and rotating them with the rotor20, the rollers 42 are carried at one end by an annular flange 48 at theend of the rotor 20. The annular flange is provided with radial slots 50at the locations of the rollers and in assembly, the rollers are droppedin the slots 50 to be held between the pistons 36 and the inner surface46 of the modulating ring. The other ends of the rollers are carried inslots 52 in an annular ring 54 which is mounted on the rotor to rotatetherewith.

The rotor is supported for rotation within the housing 8 on a ballbearing assembly 56 having bearing balls 58 held between an inner race60 and an outer race 62. The ball bearing is supported in an annularsocket 64 at one end of the housing chamber 22.

Thus, the rotor 20 rotates about a fixed axis with respect to thehousing 8, and the pistons 36 are reciprocated by being held within themodulator ring 40 which is positioned eccentric with respect to therotor. The eccentricity of the modulator ring is adjustable to vary theamount of reciprocation given the pistons and thus the output of thepump.

To control the eccentric position of the modulator ring 40, it is heldwithin a second outer ring 66 which is located within the housingchamber 22. The outer positioning ring 66 supports the inner ring by aseries of bearing rolls 68 located between the rings. The rings are thusconcentrically located with respect to each other and the inner ring isfree to rotate with respect to the fixed outer ring. The outer ring ismoved within the housing chamber 22 by a number of positioning memberswith the primary positioning members being controlled by the pressure ofthe delivery fluid.

As the rotor 20 rotates and the pistons 36 reciprocate, fluid is takenin and expelled from the cylinders 34 through the fluid deliverypassageways 38. For the intake stroke of the pistons 36, the passageways38 are in communication with an elongated arcuate slot 70 in a valveplate 72 which is spring pressed against the fiat end face 74 of therotor. Communicating with the elongated arcuate intake slot 70 is anintake passageway 76 which is formed by a connector 78 and which has anaxis parallel to the axis of rotation of the pump. The arcuate slot 70has substantially the same area as the outside diameter of the connectortubes 78, so that changes in inlet pressure will have no effect on thevalve plate rubbing force.

The connector tube 78 has an outer diameter which permits it to fitsnugly within an opening 86 within the valve plate and Within an opening82 in the housing cap. O-ring seals 84 and 86 prevent the leakage offluid as it flows into the connector tube 78. The cap has an internallythreaded passageway 88 through which the intake fluid flows on enteringthe housing. For the delivery stroke of the piston, the fluid passageway38 communicates with an arcuate slot 90 which extends around the otherhalf portion of the valve plate 72. This slot 90 leads to a deliverypassageway 94 within a projection 96 integral with the valve plate. Thearcuate slot 90 has substantially the same area as the outside diameterof the valve plate projection 96, such that change in discharge pressurewill have a minimum effect upon the valve plate rubbing pressure.

The valve plate projection 96 extends into an opening 98 in the housingcap, and the projection 96 and the connector sleeve 73 prevent the valveplate 72 from rotating with the rotor 20. The projection 96 contains acoil compression spring 100, which bears against a spring supportingwasher 102 within the opening 98 in the housing cap and urges the valveplate 72 to a non-leaking engagement with the face 74 of the rotor.Fluid under pressure is delivered from the pump through the delivery oroutlet passageway 104 in the housing cap. An 0- ring 106 seals theprojection 96 within the opening 98 of the cap.

In the position illustrated in FIGURE 3, the modulating ring 40 isshifted to the left to reduce the pump displacement and shifted to theright to increase the displacement. For movement of the modulating ringto vary the pump output, lateral forces are applied to the outer ring66. To guide the outer ring in its lateral movement within the housingchamber 22, opposed guide ascmblies 108 and 110 are provided. The guideassemblies include a ring supporting bearing member 112 for the guideassembly 108, and 114 for the guide assembly 110. An important featureof the invention is the provision of thermally expansible backingelements 116 and 118 for the guide bearings 112 and 114. The parts maybe made of different materials having dilferent rates of expansion. Forexample, the housing 3 may be of a material having a greater coefficientof expansion and as the temperature of the pump increases the guidesnormally would move away from firm contact with the ring.

The bearing rings 66 and 40 preferably are constructed of alloy steel tocarry the high contact stress and the housing is constructed of eitheraluminum or magnesium in order to minimize weight. Thus the expansion ofthe aluminum or magnesium case would be nearly double the rate of thealloy steel rings and considerable differential expansion will occur.The thermal expansive backing members are designed to have a rate ofthermal expansion so that the difference in expansion with increase intemperature of the pump will be compensated for. The backing elements116 and 118 are formed of Teflon, which is a plastic material soldcommercially under the foregoing trade name, and which has an expansionapproximately five times greater than aluminum or steel. The Teflon pads116 and 118 are held within caps 120 and 122 which are threaded andscrewed into sockets in the sides of the housing. O-ring gasket seals124 and 126 are provided to prevent leakage from the housing chamber 22.Thus, the bearing members 112 and 114 continually hold the ring 66snugly within the housing chamber preventing vibration and chatter, andpermitting the ring to be moved laterally to shift the modulating ring40.

In other words, the difference between the diameter of the outer ring 66and the diameter of the housing is taken up by the guide assemblies 108and 110. This difference will change with temperature change. Thedifference change must be equaled by the expansion and contraction ofthe pads 116 and 118 plus the expansion and contraction of the guidebearings 112 and 114. Since the expansion and contraction of the guidebearings 112 and 114 is small by comparison with the pads 116 and 118,because they are made of metal which has a low coeificient of expansionas compared with the Teflon pads 116 and 118, their expansion in manyconstructions can be ignored.

When the ring 66 and the housing are selected, the difference inexpansion per degree of temperature change can readily be determined,from either measurement or from known expansion of annular membersformed of given metals. The length of the pads 116 and 118 is thenchosen to substantially equal said dilference in expansion per degree oftemperature change. When said difference is a larger figure, the padswill be made longer, and when said difference is a smaller figure thepads are made shorter. Then, at temperatures between room temperatureand operating temperature, the pads will fill the space caused by thedifference in expansion between the ring and housing, but they will notoverfill this space and the ring will not have play but also will notbind. If the expansion and contraction of the metal bearings 114 and 116is to be taken into account, with metal bearings of a known coefficientof expansion, it is a simple matter to select a conibination of lengthsof pads and bearings which will together yield an expansion equal tosaid expansion dilference between the ring 66 and the housing 8. As analternative, a given bearing length may be selected, and when the Teflonpad length is determined, caps 120 and 122 are provided to support thepads so that the bearings are in engagement with the ring 66.

A lateral pressure of a constant force is applied to the ring 66 by aspring biasing element 128. The biasing element includes a hollow cap130 threaded into an opening in the side of the housing 8, and having acylindrical inwardly facing opening 132 in which slides a piston 134biased toward the ring 66 by a spring 136. The spring 136 applies aconstant pressure against the ring urging the modulating ring 40 towarda position of maximum displacement of the pump. Thus, when no otherforces are applied, such as when the pump is first started, a maximumdelivery will be received until pressure is built up.

Another lateral force is applied in the direction to urge the modulatingring 40 toward a position of maximum capacity of the pump by apositioning piston assembly 138. This assembly is held within a hollowboss 140 projecting from the housing 8 and facing inwardly toward thehousing chamber 22. A piston 142 is slidably mounted within a lining 144within the boss. The piston 142 has its inner end received Within ahollow sliding cup 145 also slidably mounted within the lining 144. Thepiston supporting lining 144 is threaded into the boss 140 from insidethe casing chamber 22, and is held in place by threads 146. An O-ringseal 143 prevents leakage of pressurized fluid from a space 150 behindthe piston 142. v

The space or chamber 150 behind the piston is filled with fluidcommunicated thereto from the output of the pump, and is, therefore, atthe pump delivery pressure. As shown in FIGURE 4, a fluid pressure line152 leads through a ridge 154 in the housing cap 24 and communicates atone end with the discharge passageway 104 from the pump'and at the otherend with a lateral passageway 156 which leads to the space 150 behindthe piston. Thus, the hollow sliding cup 145, is pressed against thering 66 in accordance with the output of pressure of the pump, and tendsto urge the modulating ring 40 to a position of full pump output.

A lateral force is applied against the ring 66 in an opposite directionby a feathering piston assembly 158. A feathering piston 160 is slidablyheld within a cap 162 threaded into the open end of a boss 164 on thehousing 8. Seals 166 and 168 prevent leakage of pressurized fluid fromthe chamber 170 behind the feathering piston 160 and to the housingchamber 22. The piston is provided with a piston ring 172 which preventsfluid leakage past the piston. The piston 160 bears directly against thering 66, and its position varies to vary the position of the modulatingring 40 with variance in discharge pressure of the pump. The pumpdischarge fluid is communicated to the chamber 170 behind the featheringpiston 160 through a passageway 174 formed in a rib 176 on the housingcap 24. A lateral passageway 178 leads the fluid to the chamber 170.

Fluid is admitted to the passageway 174 to control the position of thefeathering piston by an output pressure control valve assembly 180. Theoutput pres sure control valve 180 has a valve body 182 which isthreaded into a threaded opening 184 in the housing cap 24, as shown inFIGURE 4. The flow through the valve passes through an orifice 186 atthe inner end which communicates withthe pump discharge passageway 104.The orifice is'formed in an inset fitting 188 in the end of the valve180. The orifice leads to a cylindrical chamber 190 in which is locatedthe control piston 192. The piston is slidably movable within thechamber 190 to open the lateral passageway 194 and permit a flow of pumpdelivery fluid through the passageway into an annular groove 196 aroundthe valve body. The groove is in direct communication with thepassageway 174 leading to the chamber behind the feathering piston 160.Thus, when the control piaston 192 is permitted to slide rearwardly anduncover the lateral passageway 194, pressurized fluid will be permittedto move the feathering piston 160, FIGURE 3, against the ring 66 to movethe modulating ring 40 toward at position of decreased pump output. Thiswill occur when the pump output reaches the predetermined pressure atwhich the output is to be maintained. When the pressure drops below thepredetermined constant pressure, the piston 192, FIGURE 4, will coverthe lateral passageway 194. Fluid will then bleed out of the chamber 170behind the feathering piston 160 through the passageway 174, throughlateral passageway 194, and through an axially extending passageway 198through the valve body. This passageway leads to a spring chamber 200 inthe valve body and the fluid will flow into the space 202 behind thepiston and out through a lateral passageway 204 in the valve body whichcommunicates with an opening 206 draining into the housing chamber 22.The fluid pressure behind the feathering piston 160 will thus berelieved, .again permitting the ring 66 to move the modulating ring 40to a position of increased discharge. A balance is maintained at theproper discharge pressure by movement of the piston 192. Duringstarting, it will be noted in FIGURE 4 that the piston 192 coverspassageway 194 and opens bleed passageway 206. Further, it will be notedfrom FIGURE 4 that piston 192 will cover the lateral passage 204 to sealthe spring chamber 200 when pressurized fluid is being directed upthrough the passageway 174 to the feathering piston. 1

Control of the valve piston 192 is accomplished by a plunger 208controlled by a spring 210 positioned in the spring chamber 200. Theplunger 208 is slidably mounted in the spring chamber 200 and hasopenings 211 to permit the free flow of fluid to either side of theplunger. The plunger has an extension which engages the piston 192 sothat the piston is urged toward the end of the valve body 182 by thespring, and urged in the opposite direction by the pressure at the endof the piston in the chamber 190.

The spring pressure against the piston 192 is adjusted by a pressureadjusting cap 212 adjustably threaded onto a threaded end 213 of thevalve body. The cap 212 has a spring engaging member or plunger 214,which is held within a cup 216 with the bottom of the cup carrying anexpansion pad 218.

As the temperature of the parts of the pump increase, the spring modulusof the spring 210 decreases, thus decreasing the pressure of the springagainst the piston 192. To compensate for this and insure a constantspring pressure against the piston 192, the pad 218 is formed of Teflonor a like material which has a coeflicient of expansion suflicient toclose the coil compression spring 210 a distance so that its forceagainst the piston 192 will remain constant regardless of thetemperature of the pump. Thus, as the temperature of the pumpincreasesand modulus of the spring decreases, the spring will be shortened due tothe expansion of the thermal expansive pad 218. The function of this padwill remain the same for any setting of the pressure adjusting cap 212.It will be understood, however, that the thiclness of the pad chosen maybe varied to suit the pressure setting in order to get the properthermal compensation.

The pump is adapted to be used for supplying a systern wherein thedemand for pressurized fluid is intermittent, so that a constantpressure will be delivered by the pump under varying quantities ofdelivery. Under some circumstances, the system will require no fluid andthe pump will thus operate under zero delivery conditions. The frictionof the pump parts naturally creates an amount of heat and this heat isdissipated during normal operation and absorbed by the fluid passingthrough the pump. Under conditions of no delivery, a special by-passfluid is directed through the housing chamber 22 to provide the coolingnecessary.

The by-pass fluid is provided by a bypass valve assembly 220 supportedwithin a hollow boss 222 at the side of the housing 8. A valve body 224is threaded into the hollow boss 222 from within the housing 8. Thevalve body carries a valve plunger 226, which is reciprocable within thebody to control flow through a lateral passageway 228.

When the valve plunger 226 is in the position shown, the passageway 228is closed. When the valve plunger 226 moves laterally, or to the left,as shown in FIGURE 3, the passageway 228 is opened, and a flow of fluidwill be permitted from the delivery passageway 104 of the pump, FIGURE4, to the housing chamber 22. The fluid will flow through a by-passpassageway 230, formed in a rib 232 in the housing cap 24. A lateralpassageway 234 leads from the rib passageway 230 into an annular groove236, FIGURE 3, communicating with the valve passageway 228. Fluid willflow through the hollow core 238 of the valve plunger 226 and throughthe port 240 in the base of the cup 242 which is slidably mounted withinthe valve body. The cup 242 supports the flared base of the valveplunger 226 and the flared base receives the force of a coil compressionspring 244 bearing against the end of the hollow chamber 246 in thevalve body 224.

It will be observed that a position of the valve plunger 226 iscontrolled by the position of the outer ring 66 which bears against thecup 242 holding the valve plunger against its spring 244. When the ring66 is in the position wherein the pump is delivering fluid, the plunger226 closes the orifice 228. However, when the ring 66 moves to the leftfrom the position as shown in FiGURE 3, to a location where themodulating ring 40 is in a location of minimum delivery, the valveplunger 226 will uncover the passageway 228, and a flow of by-passcooling fluid will be permitted from the delivery passageway of thepump. Since this delivery passageway is connected to a supply line orsupply tank, or the like, a constant supply of fluid will be availablefor cooling the pump.

As shown in FIGURE 1, the by-pass cooling fluid will be permitted toescape from the housing chamber 22 through a passageway 247 in the pumphousing 8 leading to an internally threaded drain opening 248. Theby-pass fluid will, of course, permit lubrication for the rollerbearings 68 between the rings 40 and 66, and the ball bearingssupporting the rotor 20.

As a brief summary of operation, the rotor 20 is driven in rotationwithin the modulator ring 40 which is mounted to be moved eccentricallywith respect to the rotor. The modulator ring rotates with the rotor,being carried within bearing rollers 68 held within an outer ring 66.The inner modulator ring transmits radial forces to pistons 36 carriedin radially extending pump chambers 34 through axially extending rollers42.

The outer ring 66 is laterally positoned to vary the output of the pumpby a positioning piston 342, FlGURE 3, which receives pressure fluidwithin the piston chamber from the pump output. A variable positioningpressure is applied by a feathering piston 166 which intermittentlyreceives discharge fluid from the pump by the action of a control valve180. The feathering piston is larger than the piston 142 and therefore,applies a greater force.

A control valve has a valve piston 192 controlled by a spring 216 andalternately moves to expose a lateral passageway 194 to permit a flow offluid up to the feathering piston. A thermal expansive pad 218 maintainsthe pressure of the valve spring 210 constant regardless of temperaturechange. During periods of minimum pump delivery, a bypass of fluidthrough the housing chamber 22 is permitted the by-pass valve 220 havingthe plunger 226 which is positionally controlled by the ring 66.

Thus, it will be seen that we have provided an improved constantpressure variable displacement pump which meets the objectives andadvantages hereinbefore set forth. The pump has very important basicadvantages in that it can be constructed in a small size for operationat a high speed, and has a potential long life.

It will be understood that while the rotor and pumping means are shownin the form of a member carrying reciprocating pistons that other typesof pumping means may be employed utilizing certain features of theinvention. It will also be recognized by those skilled in the art, thatcertain other changes may be made in various operating elementsretaining the advantages of certain elements embodying the principles ofthe invention.

The pump is compact and capable of accurate control with high speedoperation and substantial delivery output. It will be recognized, thatin certain circumstances, different positioning devices for themodulator ring can be employed. Further, various elements of the pumpmay be used in different operating circumstances, although the pump isshown in its preferred environment.

We have, in the drawings and specification, presented a detaileddisclosure of the preferred embodiments of our invention, and it is tobe understood that we do not intend to limit the invention to thespecific form disclosed, but intend to cover all modifications, changesand alternative constructions and methods falling within the scope ofthe principles taught by our invention.

We claim as our invention:

1. In a variable displacement pump the combination comprising, a pumprotor carrying pumping means, an annular modulator ring positioned withits axis parallel and eccentric with respect to the rotor and operatingthe pumping means with rotation of the rotor within the ring, a housingdefining a chamber for enclosing the ring and rotor for movement of thering in the housing in a radial direction for changing the distancebetween the ring axis and rotor axis, pump output control means forshifting the ring radially within the housing, bearing guides supportedon the housing and engaging the peripheral outer surface of the ring andlocated on opposite sides of the ring laterally of the path of radialshifting movement of the ring, and a backing member between the housingand at least one of the bearing guides non-yieldably holding the guidesin engaging supporting non-binding contact with the ring and having athermal expansion rate equal to the difference between the expansionrate of the housing and the ring so that the ring will be sup portedbetween the guides at varying temperatures without the formation ofspaces between the ring and guides and without binding the ring.

2. In a variable displacement pump the combination comprising a pumpcarrying a radially reciprocating pump element, an annular modulatorring positioned with its axis parallel and eccentric with respect to therotor axis and operative to reciprocate the pump element with rotationof the rotor within the ring, a housing defining a chamber for enclosingthe ring and rotor for movement of the ring in the housing in a radialdirection for changing the distance between the ring axis and rotoraxis, said ring and said housing formed of diiterent materials withdifferent coefficients of thermal expansion, pump output control meansfor shifting the ring radially within the housing, bearing guidessupported on the housing and engaging the peripheral outer surface ofthe ring and located on opposite sides of the ring laterally of the pathof radial shifting movement of the ring, and backing members between thehousing and each of the guides nonyieldably holding the guides inengaging supporting nonbinding contact with the ring and having athermal expansion rate equal to the diiference between the expansionrate of the housing and the ring so that the ring will be supportedbetween said guides at varying temperatures without the formation ofspaces between the ring and guides and without binding the ring.

3. In a variable displacement pump the combination comprising, a pumprotor carrying radially reciprocating pump elements, an annular bearingring having an outer race and an inner race positioned with its axisparallel and eccentric with respect to the rotor axis and operative toreciprocate the pump elements with rotation of the rotor within thering, a housing defining a chamber for enclosing the ring and rotor formovement of the ring in the housing in a radial direction for changingthe distance between the ring axis and the rotor axis, pump outputcontrol means engaging the ring for shifting the ring radially withinthe housing, bearing guides supported in the housing and engaging theperipheral outer surface of a the ring and located on opposite sides ofthe ring laterally of the path of radial shifting movement of the ring,recesses in the housing supporting the bearing guides, and backingmembers in each of the recesses behind the hearing guides non-yieldablyholding the guides in engaging supporting non-binding contact with thering and having a thermal expansion rate equal to the difference betweenthe expansion rate of the housing and the ring so that the ring will besupported between said guides at varying 10 temperatures without theformation of spaces between the ring and guides and without binding thering.

4. A combination of elements in a variable displacement pump inaccordance with claim 3 in which the backing members are formed ofTeflon.

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